class Student:
    def __init__(self, name, age):
        self.name = name
        self.__age = age

    @property
    def age(self):
        return self.__age

    @age.setter
    def age(self, age):
        self.__age = age

    def __str__(self):
        return '我叫{}，今年{}岁'.format(self.name, self.__age)


s1 = Student('小明', 20)
print(s1.__dir__())
print(s1)
s1.age = 25
print(s1)
